Leonardo da Vinci’s aerial screw design required four operators to turn its mechanism.
The aerial screw is a Renaissance flying-machine concept usually dated to around 1489 or 1490. Leonardo imagined a large helical surface made from reeds and covered with linen. Four people would stand on a platform and turn cranks connected to the central shaft, causing the screw to rotate.
Leonardo reasoned that the rotating screw could press against the air and lift the machine. No evidence shows that the device was ever built or flown, and the human power available would not have been sufficient for a practical aircraft of the proposed size.
The machine is often called a helicopter because its shape resembles a modern rotorcraft. That comparison is useful as a visual analogy, but Leonardo’s design had a rotating helical screw rather than the powered rotor and control systems used by helicopters.